1. Field of the Invention
The present invention relates to methods and apparatus used in the completion of a well. More particularly, the invention relates to downhole tools. More particularly still, the present invention relates to downhole tools having a sealing and anchoring assembly.
2. Description of the Related Art
Hydrocarbon wells are typically formed with a central wellbore that is supported by steel casing. The casing lines a borehole formed in the earth during the drilling process. An annular area formed between the casing and the borehole is filled with cement to further support the wellbore. Typically, wells are completed by perforating the casing of the wellbore at selected depths where hydrocarbons are found. Hydrocarbons migrate from the formation through the perforations and into the wellbore where they are usually collected in a separate string of production tubing for transportation to the surface of the well.
Downhole tools with sealing systems are placed within the wellbore to isolate producing zones or to direct the flow of production fluids to the surface. Examples of sealing tools include plugs and packers. The sealing tools are usually constructed of cast iron, aluminum, or other drillable alloyed metals. The sealing system includes a sealing element that is typically made of a composite or elastomeric material that seals off an annulus within the wellbore to prevent the passage of fluids. Upon actuation, the sealing element is axially compressed, thereby causing the sealing element to expand radially outward from the tool to sealingly engage a surrounding surface of the tubular. In one example, a bridge plug is placed within the casing to isolate upper and lower sections of production zones. By creating a pressure seal in the wellbore, bridge plugs allow pressurized fluids or solids to treat an isolated formation.
Packers are typically used to seal an annular area formed between two co-axially disposed tubulars within a wellbore. For example, packers may seal an annulus formed between the production tubing and the surrounding wellbore casing. Alternatively, packers may seal an annulus between the outside of a tubular and an unlined borehole. Routine uses of packers include the protection of casing from well and stimulation pressures, and the protection of the wellbore casing from corrosive fluids. Other common uses include the isolation of formations or leaks within a wellbore casing or multiple producing zones, thereby preventing the migration of fluid between zones.
In some applications, it is desirable to install a bridge plug within a large diameter tubular at a point or depth below which a small diameter tubular has previously been installed, e.g., installing a bridge plug in a casing string disposed below a production tubing. In such applications, the sealing element is expanded to a greater distance in order to complete the seal. As a result, the strength of the seal may be compromised and the conventional sealing tool may experience increased failure.
Bridge plugs with inflatable resilient members or bladders were developed to overcome these deficiencies. Inflatable bridge plugs are typically designed with a sufficiently small outside diameter to permit passage through the tubing string and thereafter, when positioned within the larger internal diameter casing, may be inflated to form a sealing bridge plug within the casing. On occasions, the inflatable members or bladders are furnished with anchoring stays designed to grip the internal diameter of the casing and prevent the inflated bladder from movement within the casing. However, under prolonged and cyclic operations within the well, inflatable bridge plugs have tended to fail, sometimes due to a malfunction of their valving systems which maintain the inflation. More commonly, inflatable bridge plugs fail due to failure of the bladder, which commonly results from delamination or puncture of the resilient bladder, thereby causing the bladder to deflate and cease to function as a bridge plug within the casing.
There is a need, therefore, for a sealing apparatus for high expansion applications. There is a further need for a sealing apparatus that may travel through a smaller diameter tubular and seal off a larger diameter tubular.
The present invention generally relates to a method and apparatus for sealing a tubular. In one aspect, the present invention provides for a sealing apparatus having a body and a sealing system disposed about the body. The sealing apparatus further includes one or more extrusion rings disposed at each end of the sealing system, wherein each of the one or more extrusion rings includes a plurality of slots. Preferably, the slots of each extrusion ring are staggered against the slots of another extrusion ring. The sealing apparatus may also have a cone to support the one or more extrusion rings and urge a slip member outward. The slip member is disposed adjacent the cone at each end of the sealing system. Upon actuation, the sealing apparatus expands the sealing system and causes the slip member to fold outward and engage the tubular.
In another aspect, the sealing system includes one or more sealing elements. In one embodiment, the sealing system has a center seal element, a middle seal element, and an end seal element. Preferably, the seal elements are designed to urge end seal elements outward. Additionally, the middle seal elements is made of a harder material than the end seal elements.
In another aspect still, the sealing apparatus may further include a backup ring disposed between the one or more extrusion rings and the cone. The sealing apparatus may also have an expansion cone disposed between the cone and the slip member. In one embodiment, the expansion cone is connected to the cone using a first shearable member. Also, the slip member is connected to the expansion cone using a second shearable member. Preferably, the first shearable member shears at a lower force than the second shearable member. In this manner, the setting sequence of the sealing apparatus may be controlled.
In another aspect, the present invention provides for a sealing apparatus having a body and a sealing system disposed about the body. The sealing apparatus further includes one or more extrusion rings disposed at each end of the sealing system. The sealing apparatus may also have a first cone to support the one or more extrusion rings and a second cone expandable over the first cone. A slip member is disposed adjacent the second cone at each end of the sealing system. Upon actuation, the sealing apparatus expands the sealing system and causes the slip member to fold outward and engage the tubular.
Aspects of the present invention further provide a method of sealing a tubular. Initially, a tool having a sealing member disposed about a body is run into a tubular. The tool may also have an extrusion ring disposed adjacent each end of the sealing member and a cone disposed adjacent each extrusion ring. Each end of the tool has a slip member for anchoring the sealing system. After the tool in disposed at the desired depth of the tubular, a force is applied to the slip member at one end of the tool. The force causes the sealing member to expand into contact with an area of the tubular, the extrusion ring to fold outward and plastically deform, and the slip member to expand and engage the tubular. Preferably, the sealing member, extrusion ring, and the slip member are set in a predetermined sequence.
In another aspect, the expansion packer is capable of expanding at least 15% diametrically to seal a tubular.